1. Field of the Invention
The present invention relates to waveguide-type coupler/splitters effectively used in an optical fiber communication system and optical sensor system, and more particularly, to waveguide-type coupler/splitters which need not be connected with any other optical parts, such as an optical wavelength division multiplexer/demultiplexer, at the time of optical line monitoring in these systems.
2. Description of the Prior Art
In an optical fiber communication system, such as the one shown in FIG. 1, a signal transmitted from one parent station 1 is divided into N number of signals by means of a 1-input/N-output waveguide-type coupler/splitter 2, and the individual signals are distributed to N number of child stations 4.sub.1, 4.sub.2, . . . 4.sub.N by means of N number of fiber lines 3.sub.1, 3.sub.2, . . . 3.sub.N, respectively.
Referring now to FIGS. 2 to 7, 1-input/16-output versions of the coupler/splitter 2 adapted to be used in this system will be described by way of example.
A coupler/splitter A of the type shown in FIG. 2 uses, as each of its element coupler/splitters, a 1-input/2-output Y-branch waveguide I in which two output ports I.sub.b and I.sub.c are continuous with an input port I.sub.a, as shown in FIG. 3. The input and output ports I.sub.a, I.sub.b and I.sub.c of these individual element coupler/splitters are concatenated to one another in four stages in a tournament-list style.
A coupler/splitter B of the type shown in FIG. 4 uses, as each of its element coupler/splitters, a 1-input/2-output directional connector II formed of a 1-input/2-output Y-branch waveguide and having a junction II.sub.d at which one of two waveguides is continuous and the other is discontinuous, as shown in FIG. 5. Input and output ports II.sub.a, II.sub.b and II.sub.c of these individual element coupler/splitters are concatenated to one another in four stages.
A coupler/splitter C of the type shown in FIG. 6 uses, as each of its element coupler/splitters, a 1-input/2-output directional coupler III formed of a 1-input/3-output Y-branch waveguide and having a junction III.sub.d at which two waveguides are discontinuous with another waveguide, as shown in FIG. 7. Input and output ports III.sub.a, III.sub.b and III.sub.c of these individual element coupler/splitters are concatenated to one another in four stages.
In monitoring the optical fiber lines 3.sub.1, 3.sub.2, . . . 3.sub.N without interrupting communication between the parent station and the child stations 4.sub.1, 4.sub.2, . . . 4.sub.N, in the optical communication system shown in FIG. 1, it is necessary to connect an optical line monitoring device (e.g., OTDR) 5, which uses light with a monitoring wavelength .lambda..sub.2 different from a communication wavelength .lambda..sub.1, as shown in FIG. 8, to the arrowed spot (FIG. 1) of an optical path connecting the parent station 1 and the 1-input/N-output coupler/splitter 2, through an optical wavelength division multiplexer/demultiplexer 6 for synthesizing and dividing light waves with the wavelengths .lambda..sub.1 and .lambda..sub.2.
Thus, when using the 1-input/N-output coupler/splitter 2 composed of the concatenated 1-input/2-output element coupler/splitters I, II or III of the conventional configuration described above, the interposition of another optical part, such as the optical wavelength division multiplexer/demultiplexer (.lambda..sub.1 .noteq..lambda..sub.2) or an optical coupler (.lambda..sub.1 =.lambda..sub.2), is required in connecting the optical line monitoring device 5 between the coupler/splitter 2 and the parent station 1.